Include a personal greeting, thank you message mentioning the specific item or service, the impact made by the gesture, future action and a personal closing. The key to writing a professional thank-you note is being as specific as possible to make the recipient understand how appreciative you are.
Address the greeting to a specific individual to give the note a personal feeling. Open with a line or two of thanks, mentioning the gift, service or gesture specifically so the recipient knows exactly why you're thanking her. This also shows you took the time instead of rushing with a general thank-you letter.
Continue with specific ways the item or gesture helped you, perhaps with financial backing or training that improves your business processes. If you plan to follow up with the person, include specifics such as calling, visiting or referring the person to other colleagues.